The new viruses are variants of the self-replicating Melissa, which wreaked havoc earlier this year, clogging corporate email servers. The virus uses a combination of Microsoft Word and Outlook software to spread itself to people on a computer's email address list.
Earlier this month, PC users reported a resurgence of a virus which works in a similar fashion to Melissa, named VBS.freelink.
The new versions of Melissa also exploit Word and Outlook. Emails containing the virus come with an attachment. If the attachment gets clicked, the virus sends out emails to anyone listed in the recipient's Outlook address book. In addition, both new viruses attempt to delete various system files and folders.
Network Associates, which sells anti-virus software and watched sales skyrocket as a result of the Melissa outbreak, called the new viruses a "medium" risk. "The fact that the variants spread rapidly via email, delete data, and have been seen in the wild have prompted the assessment," the company said in a statement.
Computer users with updated anti-virus software will be protected against the new viruses, according to Network Associates.
A New Jersey man, David L. Smith, was arrested and charged with disseminating the original Melissa virus.